Last reply is most likely involved in what I did just recently, It's always very good to look in the top left corner of the site before posting to see if it says "Offline" or "Online" without any player count next to it, most likely means it just restarted or is offline. however I cannot tell for certain if the OP was having the issue I looked into earlier today.
Noticed Fluorite plains acting up and wouldn't accept anyone to connect to it but also Lonely cave, we had a quick server restart and that fixed the issue from what I can see. Shouldn't really be a problem anymore, if it is it wouldn't be server sided at least.